Caspase 9 is a member of the CED-3 subfamily of the caspase family of cysteine proteases that play an essential role in the execution phase of apoptosis. These enzymes share a dominant primary specificity for cleaving bonds following aspartic acid residues. Initiator caspases (such as caspase 8) activate effector caspases, such as caspases 3 and 7. The effector caspases then cleave cellular substrates ultimately leading to the morphological changes of apoptosis. (Ac-LHED)2-R110 is a selective fluorogenic substrate for caspase 9. The caspase 9-induced hydrolysis of (Ac-LHED)2-R110 results in the release of AMC fluorophore that is detected using an excitation wavelength of ~490 nm and an emission wavelengh of ~520 nm. The assay can be run in the assay buffer consisting of 50 mM MES, pH 6.5, 10% PEG 8000, 0.1% CHAPS, 5 mM DTT, and 1 mM EDTA.